﻿using System;

namespace _010.字符出现的次数
{
	internal class Program
	{
		static void Main(string[] args)
		{
			string str = Console.ReadLine();
			// 计数 保存每一个字符出现的次数
			int[] countArray = new int[26];
			for (int i = 0; i < str.Length; i++)
			{
				countArray[str[i] - 'a'] = countArray[str[i] - 'a'] + 1;
			}

			bool isFind = false;
			char c = ' ';
			for (int i = 0; i < str.Length; i++)
			{
				if (countArray[str[i] - 'a'] == 1)
				{
					isFind =  true;
					c = str[i];
				}
			}
			if (isFind)
			{
				Console.WriteLine(c);

			}else
			{
				Console.WriteLine("no");
			}

		}
	}
}
